Many consumers have long had the desire to lighten their hair color because a blond hair color is considered to be attractive and desirable from a fashion standpoint. For this purpose, various hair bleaching agents with different bleaching capabilities are available on the market. The oxidizing agents contained in these products are capable of lightening hair fibers by oxidative destruction of endogenous melanine pigment. For a moderate hair bleaching effect, it is sufficient to use hydrogen peroxide alone—optionally also with ammonia or other alkalizing agents—as the oxidizing agent. To achieve a stronger hair bleaching effect, a mixture of hydrogen peroxide and at least one compound selected from percarbonates and peracids, in particular peroxodisulfate salts and/or peroxomonosulfate salts, is used in general. To increase the hair bleaching effect, the agents contain greater use concentrations of hydrogen peroxide and percarbonates or peracids, in particular persulfates. Dark hair, dark brown hair or black hair can thus be lightened by four to six shades in one step. The hydrogen peroxide and the percarbonates or peracids are stored separately from one another until used, so as not to deactivate the percarbonates or peracids prematurely. The hydrogen peroxide component, comprising an aqueous solution of hydrogen peroxide, has an acidic pH to stabilize the hydrogen peroxide.
For the melanine-degrading effect of hydrogen peroxide and the hair bleaching effect on keratinic fibers, however, it is advantageous if the application mixture of hydrogen peroxide solution and persalt has an alkaline pH.
There are various possibilities to achieve an alkaline pH of the lightening application mixture:
The hair bleaching agent contains at least one powdered alkalizing agent in a total amount, such that the application mixture has the desired alkaline pH,
or
the hydrogen peroxide solution is additionally combined with an alkalizing agent preparation for the application mixture.
However, lightening of hair is also associated with damage to hair because there is oxidative damage not only to the hair pigment but also to the structural components of hair. Depending on the manifestation of the degree of damage, it ranges from coarse, brittle and difficult-to-comb-out hair to hair with a reduced resistance and tear strength or even to breakage of hair. The greater the amount of hydrogen peroxide and optional persalts or percarbonates used, even greater damage is therefore usually done to the keratin fibers.
Various methods have been used to minimize the damage to hair and to compensate for the damaging effect of the oxidizing agents.
EP 1022014 A1 describes an acidic hair coloring agent, which contains an alkylene carbonate and is optionally adjusted to an acidic pH with organic dicarboxylic acids.
DE 102010063370 and DE 102005013488 disclose the use of solubilizers based on acylpyridinium derivatives to improve the lightening effect of hair bleaching agents, so that the required amount of damaging substances to be used can be reduced. DE 10008640 discloses a hair bleaching method under acidic conditions, which also reduces hair damage. However, the oxidizing agent is typically less reactive here than under alkaline conditions, so that the efficiency of the hair bleaching method can be limited. WO 2017/085117 discloses hair bleaching agents in which a gentle lightening of the hair is made possible with the addition of certain amino acids with dicarboxylic acids. Although good results are achieved even with the methods described here, there still remains a wide range for improvements.